The present invention generally relates to sector mark detection apparatuses and optical disk access apparatuses, and more particularly to a sector mark detection apparatus which detects sector marks recorded on an optical disk and an optical disk access apparatus which uses a sector mark detection apparatus.
Conventionally, in recording mediums such as optical disks on which information can be recorded and reproduced therefrom, an address signal is recorded to indicate an address on a track of the optical disk. The address signal is recorded on the tracks in regions which are called sectors and are formed to predetermined lengths at predetermined intervals. A sector mark is added to a head of each sector, and an access to a desired sector on the optical disk is made by detecting the sector mark. The sector mark is determined by standards such as the standard decided by the European Computer Manufacturers Association (ECMA).
FIGS. 1 and 2 are diagrams for explaining examples of the conventional sector mark detection circuits.
In the sector mark detection circuit shown in FIG. 1, signals which are included in an input signal IN and have predetermined patterns are respectively detected in pattern detectors 11 and 12, and output detection signals of the pattern detectors 11 and 12 are respectively input to delay circuits 13 and 14. The delay circuits 13 and 14 supply to a threshold value circuit 15 delayed signals after predetermined times. The threshold value circuit 15 outputs a signal which indicates that the sector mark has been detected if a number of times the delayed signals match the output detection signal of the pattern detector 11 exceeds a threshold value.
On the other hand, in the sector mark detection circuit shown in FIG. 2, the delay circuits and the like shown in FIG. 1 are simplified. In other words, the input signal IN is once input to a shift register 16, sampled by a clock CLK with which a sufficient resolution can be obtained, and output to a matching circuit 17 as parallel output signals "a". The matching circuit 17 determines whether or not each of the sampled values match a predetermined pattern, and supplies to a threshold value circuit 18 signals b1 through b5 which indicate the results of the matching. If the majority of the signals b1 through b5 indicating the match is greater than or equal to a threshold value, the threshold value circuit 18 outputs a signal which indicates that the sector mark has been detected.
The sector mark detection circuits shown in FIGS. 1 and 2 are described in a Japanese Laid-Open Patent Application No.64-13263.
However, in the optical disk which is recorded according to the MCAV (Modified Constant Angular Velocity) system, a reference clock used for the recording and reproduction differs depending on the zone (or region) of the optical disk and the reference clock signal frequency becomes higher towards the outer periphery of the optical disk. For this reason, problems occur when detecting the sector marks of such an optical disk by sampling the sector marks within zones having an unknown data rate at the same sampling frequency using the sector mark detection circuits shown in FIGS. 1 and 2. More particularly, it is necessary to provide a number of matching patterns corresponding to the number of zones and to provide delay times of each of the delay circuits in the case of the sector mark detection circuit shown in FIG. 1. On the other hand, it is necessary to provide a number of matching values equal to the number of zones and corresponding to each of the sector marks in the case of the sector mark detection circuit shown in FIG. 2.
Therefore, there were problems in that the circuit construction of the sector mark detection circuit becomes complex, and that the sampling frequency must be set to an extremely high frequency in order to distinguish the zones from the matching values.